1. Field of the Invention
The invention relates to the use of esters of sulfonic acids as anti-sludge agents in acid environments and more particularly to the use of the combination of alkoxylated esters of alkyl benzene sulfonic acids with non-ionic dispersants to reduce the formation of sludge arising out of the acid stimulation of oil containing formations.
2. Description of the Prior Art
Mineral and/or organic acids are used to stimulate limestone, dolomote and sandstone hydrocarbon bearing formations. The function of the acid is to dissolve acid soluble materials so as to clean or enlarge the flow channels of the formation leading to the wellbore, allowing more oil and/or gas to flow to the wellbore.
There are problems caused by the interaction of the stimulation acid and certain crude oils in the formation to form sludge. Interaction studies between sludging crude oils and the introduced acid show that permanent rigid solids are formed at the acid oil interface when the aqueous phase is below a pH of about 8. No films are observed for non-sludging crudes with acid.
These sludges are usually reaction products formed between the acid and the high molecular weight hydrocarbons such as asphaltenes, resins, etc.
Once the sludges are formed they are difficult to remove or control. These sludges cause damage to the wellbore generally manifesting itself as a very thick emulsion. It has been suggested that the best solution to the sludge problem is to prevent sludge formation (see Formation, Effect and Prevention of Asphaltene Sludges During Stimulation Treatments by E. W. Moore et al., Journal of Petroleum Technology, Sept. 1965 pp 1023-1028).
Present methods for preventing or controlling sludge formation with the attendant flow problems during the acidization of crude containing formations include adding "anti-sludge" agents to prevent or reduce the rate of formation of crude oil sludge which stabilizes the acid-oil emulsion and include alkyl phenols, fatty acids, and surfactants. Frequently used as the surfactants is a blend of a sulfonic acid derivative and a dispersing surfactant in a solvent. Such a blend generally has dodecyl benzene sulfonic acid (DDBSA) or a salt of it as the major dispersant, i.e. anti-sludge, component. Formulations containing DDBSA have the following problems:
(1) because of the acid's strongly anionic character, it is incompatible with other additives to be used in the blend; PA1 (2) it has poor dispersibility in acids and brines; and, PA1 (3) it is quite corrosive to the metals and humans.
It is therefore, an object to this invention to provide an anti-sludge/demulsifier agent which overcomes the problems resulting from the presence of DDBSA.